A moving vehicle, such as an automobile, truck, bus, motorcycle or railroad car, requires at least a minimum braking distance to stop after vehicle brakes are applied and an additional time and equivalent perception-reaction distance for the vehicle driver to perceive and/or react and to apply the brakes. Each of the braking distance and the perception-reaction distance increases with vehicle velocity and may be different for different vehicles and for different drivers. Where a first vehicle immediately follows a second vehicle in a traffic lane on a highway, expressway, street, lane or road ("road"), safe operation of the first vehicle requires keeping some distance between the first and second vehicles. Many drivers use an approximately fixed separation distance from the preceding vehicle, and this distance (often as small as two vehicle lengths) does not vary with vehicle velocity, with the type of vehicle, with road conditions or with the driver.
Monitoring of vehicle velocities, vehicle spacings and the like, that control access to a specified zone, is disclosed in several U.S. patents. Most of these patents do not concern separation of two consecutive vehicles with reference to the individual velocities of the two vehicles.
What is needed is a system for creating and subsequently monitoring a variable vehicle-to-vehicle buffer zone or separation distance whose location moves with the vehicle and whose size and/or character can change with vehicle velocities, with road conditions and with other variables. Preferably, the system should determine and take account of the velocities of each of the two vehicles and should permit receipt of information, received from a central station or elsewhere, that may affect determination of the size of the vehicle buffer zone.